1. Field of the Invention
The present invention relates to a communication apparatus and, more particularly to a communication apparatus which is connected with a line together with telephone sets.
2. Related Background Art
As a communication apparatus, which can be connected with a telephone set through a telephone terminal, a facsimile apparatus, for example, has been known so far.
In this type of apparatus, singular or plural telephone sets are connected, and the line is jointly used by a facsimile apparatus and telephone sets by utilizing an outgoing and incoming control unit, a network control unit, etc. of the facsimile apparatus. As patents or patent applications for such an apparatus, U.S. Pat. No. 4,825,461; U.S. patent application Ser. Nos. 453,364 (refiled on Dec. 20, 1989); 106,783 (filed on Feb. 15, 1988); 470,461 (refiled on Mar. 13, 1991); and 465,652 (refiled on Jan. 22, 1990) have been filed.
When, however, a plurality of telephone sets are connected with the facsimile apparatus, there has been a problem that all telephone sets always ring even if one of the telephone sets is determined which is answered by an operator on receipt of an incoming call, and it is troublesome.
Also some facsimile apparatuses having an automatic TEL/FAC switching function are known in which whether the partner station is a voice terminal or facsimile terminal is automatically identified on receipt of an incoming call and the line is switched to either the facsimile apparatus or the telephone set accordingly. As patents concerning such an automatic TEL/FAX switching, U.S. Pat. Nos. 4,677,660; 4,815,121; 4,800,439; 4,932,048 and 4,916,607 have been issued.
Moreover, U.S. patent application Ser. No. 573,684 (filed on Aug. 28, 1990) has been filed for a new automatic TEL/FAX switching system, and this system is shown in FIG. 3.
In FIG. 3, a plurality of sub-telephone sets are connected with a facsimile (FAX) apparatus, which detects an incoming call. When the FAX apparatus detects a calling signal from the office exchange at time T1, the NCU of the FAX apparatus catches the line at time T2, and detects a received signal from the partner station while transmitting a ring back tone RBT during the consecutive period t1.
In the period t1, the FAX apparatus detects a procedure signal such as a voice signal or a FAX calling signal by frequency discrimination, etc. When a FAX procedure signal is detected, the FAX communication is started. When, on the other hand, a voice signal is detected or a FAX procedure signal cannot be detected within the period tl, all the connected telephone sets (1, 2) are called in a period t3 (for example, ball ringing B is executed).
A telephone line can be jointly used for both voice and data communications in the above system. But, in the case of the voice communication, it always takes a fixed time to switch to the telephone set, increasing the communication time and cost. Also when a plurality of telephone sets are connected, there is a problem in which all the telephone sets are called.